The present invention relates to an aluminum alloy blank for a lithographic printing plate and an aluminum alloy support for a lithographic printing plate having excellent electrochemical surface roughening properties, and to manufacturing methods thereof.
Presensitized plates including supports made of aluminum plates are widely used in offset printing.
In general, a flat-rolled plate having a thickness of 0.1 to 0.5 mm has been conventionally applied to an aluminum alloy blank for use in a support for a lithographic printing plate.
JIS 1000 series materials and JIS 3000 series materials are frequently applied to Al materials used herein.
A typical method conventionally used for manufacturing such an aluminum alloy flat-rolled plate includes the steps of polishing and removing surfaces of an ingot obtained by semicontinuous casting (direct chill (DC) casting), subjecting the ingot to a homogenization treatment as appropriate, performing hot rolling at given temperature, performing a heat treatment called intermediate annealing either after performing the hot rolling or in mid-course of performing cold rolling, and then performing final cold rolling.
Generally, a typical method known for manufacturing a presensitized plate includes the steps of obtaining a support for a lithographic printing plate by subjecting a surface of a sheet-type or coil-type aluminum plate to a surface roughening treatment and an anodic oxidation treatment, then forming an image recording layer by coating a photosensitive solution on this support and drying the photosensitive solution, and cutting the support into desired sizes as appropriate. After printing an image, this presensitized plate is subjected to development and formed into a lithographic printing plate.
In this method, a surface roughening treatment electrochemically performed in an acidic solution (hereinafter referred to as an “electrolytic surface roughening treatment” in this specification) is effective in order to improve adhesion of the image recording layer to the support. Alternatively, it is also effective to perform a surface treatment or to coat an undercoating solution after the anodic oxidation treatment.
When performing the surface roughening treatment including the electrolytic surface roughening treatment, minute irregularities (pits) are formed on the surface of the support. It has been conventionally considered that, by rendering diameters of the pits uniform and large or rendering depths of the pits smaller, adhesion between the recording layer and the support at an image area was strengthened and the recording layer was not peeled off even after printing numerous sheets; meanwhile, a non-image area could hold a large quantity of a fountain solution on a surface and stains hardly occur. In this way, it has been considered possible to obtain a presensitized plate which has excellent print quality. Methods for improving shapes and uniformity of electrolytically surface roughened pits from the above-mentioned viewpoints have been disclosed in JP 2000-108534 A, JP 2000-37965 A and JP 2000-37964 A, for example.
However, these methods are studied on materials having high Al purities and are therefore inapplicable to Al materials having high degrees of alloy components.
For an application to materials having high degrees of alloy components, claim 1 of JP 7-173563 A (corresponding to EP 0640694 A) discloses an electrolytically surface roughened aluminum alloy blank for a lithographic printing plate having an excellent electrolytic surface roughening property, which is a continuously cast flat-rolled aluminum alloy plate containing 0.20 to 0.80 wt % of Fe, and the balance being aluminum, crystal grain refining elements, and unavoidable impurity elements. Here, among the impurity elements, a content of Si is equal to or below 0.3 wt % and a content of Cu is equal to or below 0.05 wt %. Moreover, a solid solution amount of Fe is equal to or below 250 ppm, a solid solution amount of Si is equal to or below 150 ppm and a solid solution amount of Cu is equal to or below 120 ppm.
However, the alloy component elements include those which are solid solved in Al, those which are deposited as metal components, and those which exist as intermetallic compounds, and the amounts of the intermetallic compounds must be equal to or below given amounts. Accordingly, maintaining the low solid solution amounts of Fe, Si, and Cu as in this technique increases the deposited components and thereby causes disadvantages such as deterioration in resistance to aggressive ink stains. Further, it is difficult to maintain the low solid solution amounts while uniformly and finely crystallizing second phase grains. Here, the “aggressive ink stains” are stains of dot or annular shapes appearing on a printed sheet and the like, which are attributable to the ink attached more frequently to a non-image surface area of a lithographic printing plate as a result of several interruptions in the course of printing.
Meanwhile, there is other related art which discloses a lithographic printing plate having excellent handling characteristics in which a direction of rolling of an aluminum flat-rolled plate can be easily determined (JP 2002-79770 A).
Both ends of the lithographic printing plate are bent after the plate making process for forming the image thereon. Then, the lithographic printing plate is attached mechanically to a plate cylinder of a press. As the press continues printing with the lithographic printing plate, the fixing parts may be deformed or broken, and thereby causing printing defects such as misalignment. Otherwise, the bent portions may crack (hereinafter referred to as “corner cracks”) and preclude printing any longer. Correspondingly, there has been disclosed a technique for improving resistance of an aluminum plate to metal fatigue by controlling alloy contents within specified ranges (JP 3-11635 B). However, an aluminum plate exhibits different strength properties between the rolling direction and the orthogonal direction thereto. Even though the above-mentioned problem may be usually avoided by this technique, however, if a lithographic printing plate made of such an alloy is used in the wrong orientation (i.e., by 90°) in the course of the plate making process or attachment to the press, the lithographic printing plate may be bent in the fragile orientation along the rolling direction. The lithographic printing plate thus attached to the press may crack similarly. Therefore, there is a demand for a lithographic printing plate which can avoid misrecognition of the orientation in the course of the plate making process or attachment to the press.
Meanwhile, numerous methods have been disclosed in order to provide numbers, characters, patterns, designs, and the like on a surface of a lithographic printing plate on an opposite side of a surface coated with a photosensitive layer. For example, JP 7-76800 A and JP 6-286352 A disclose a method of performing an electrochemical surface roughening treatment on a surface of a support for a lithographic printing plate without provision of a photosensitive layer (such a surface will be herein after referred to as a “rear surface”, which may be also applied to a relevant surface of a lithographic printing plate similarly). JP 7-205563 A discloses a method of performing an alkali etching treatment on the rear surface of a support for a lithographic printing plate. JP 6-305271 A and the like disclose a method of performing a press treatment on the rear surface of a support for a lithographic printing plate by use of a transfer roller. Meanwhile, JP 6-73478 A discloses a method of providing an aluminum alloy plate with discontinuous patterns in certain colors by use of an anodic oxidation treatment. Nevertheless, all these methods entails the treatment process such as the electrochemical surface roughening treatment, the alkali etching treatment, the press treatment using the transfer roller, or the anodic oxidation treatment. As a result, fabrication of the lithographic printing plate provided with provision of the numbers, characters, patterns, designs, and the like on the rear surface according to any of these methods would incur an unfavorable process increase.
According to the related art, it has not been possible to obtain a support for a lithographic printing plate from an Al plate having high contents of alloy component elements, which has a uniform electrolytically roughened surface and allows simplification of manufacturing processes and reduction in manufacturing costs and manufacturing time.